STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Cardiac muscle. Coloured scanning electron micrograph (SEM) of cardiac muscle (green) from a healthy human heart. Between the bundles of muscle fibrils, or myofibrils, is a network of connective tissue (brown), which is mainly composed of collagen. Near bottom centre, red blood cells are seen in a blood vessel. Cardiac muscle is under subconscious control and continuously contracts to pump blood around the body without tiring.
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